Process for separating wax from oil



Malh 8, 1949- P. s. BACKLUND ETAL PROCES-S FOR SEPAHATING WAX FROM OIL Filed Feb. 6, 1945 Patented Mar. 8, 1949 PROCESS FOR SEPARATING WAX FROM OIL Peter Stanley Eacklund and Byron M. Beildeck,

Los Angeles, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application February 6, 1945, Serial No. 576,479

(Cl. ISS-18) 6 Claims. 1

This invention relates to the separation of oil and wax from wax-oil mixtures such as waxy oils or oily waxes. rlhe invention relates particularly to a process for separating Wax and oil from a wax-oil mixture to produce a low pour point oil and high melting point wax.

In a conventional process for separating wax from oils, the oil is dissolved in a solvent or a mixture of solvents at an elevated temperature and the solution then chilled to a sufciently low temperature to bring about the precipitation of the wax which may be subsequently removed by ltration, centrifuging or the like. The solvents employed in this process are those which show a preferential solubility for oil over Wax at the dewaxing temperature, such as various mixtures of benzene and acetone, benzene and methyl ethyl ketone, propane, naphtha and the like. These solvents, being very fluid at low temperatures reduce the viscosity of the oil to such an extent that very low temperatures may be employed during the filtration and as a result low pour point oils will be obtained. In this method of dewaxing, washing of the wax cake on the lter with fresh cold solvent is usually carried out. However, the type of wax cake obtained in the operation wherein the wax is precipitated out from a solvent-oil mixture by chilling is very voluminous, and susceptible to cracking during Washing, retaining a large percentage of solvent and oil and because of its structure is difficult to wash free thereof. It is not unusual for the wax cake obtained in this type of operation to contain as much as 60% by weight of oil after removal of solvent. The weight of solvent present in the so-called dry cake is usually from two to four times that of the Wax present. With many types of oils and solvents, it is necessary to add crystallization modifiers to the oil before chilling the waxy-oil solution in order to obtain a slurry which may be filtered or otherwise separated at an economical rate.

rEhe wax thus obtained being a composite of the entire wax content of the oil processed and containing, as pointed out above, large percentages of oil and solvent must be further treated in a deoiling process to remove said oil and to yield a marketable wax. Further, if it is desired to resolve the Wax thus obtained into a high melting point wax and a low melting point wax, it is necessary by recrystallization or filtration to fractionate this material.

A more recent advancement in the art of dewaxing of oils or deoiling of waxes, involves What may be termed the limited dilution principle and is often referred to as a reverse dewaxing process. This process consists essentially of chilling the wax-oil mixture prior to the addition thereto of all of the necessary solvent required for efficient filtration which chilling may be accomplished in one or more stages with intermediate addition of predetermined proportions cf the desired solvent at each stage. By operating in this manner very little of the crystallized wax will be redissolved by the solvent and a slurry is formed which filters very rapidly, yielding a more compact wax cake which will not crack during ltration or while washing with the solvent. In this manner it is possible to separate high melting point waxes, i. e. having an A. S. T. M. melting point above about F., from a wax-oil mixture in the form of large, well-defined, oil-free crystals which will result in the production in the initial stage of the operation of high melting point wax containing less than 1% of oil. In the second stage of such operation the solvent-oil mixture is further chilled and filtered yielding a low oil content, low melting point wax, i. e. below about 130 F. melting point and a wax-free low pour point oil. This type of operation, and the many modifications thereof are described fully in United States Patent No. 2,229,658.

The advantages of this reverse dewaxing or deoiling process are immediately apparent for its simplicity of operation and quality of the products obtained. However, we have found that when employing stocks of comparatively low wax content, as for example, below about 10% of high melting point wax, considerable difculty is experienced in producing therefrom a low pour point oil and an oil-free wax. Many Eastern and Mid-Continent wax-oil fractions, and particularly those which have been steam refined, are found to fall into this category. The difficulty encountered in processing these stocks by the reverse process consists of the formation on the filter and particularly on rotary filters of only a thin non-porous cake of wax, which is not only diflicult to remove from the filter, but also tends to give poor iilterability and a high oil content.

It is therefore an object of our invention to separate wax-oil mixtures into their constituent components in a simple and economical manner.

It is a more particular object of our invention to efiiciently separate wax-oil mixtures which by virtue of their relatively low wax content are diflicult to separate by conventional methods.

An important object of our invention resides in forming within the Wax-oil mixture of low content the same type of desirable waxcrystal structure developed when crystallization occurs in a wax-oil mixture of higher wax content, which crystallization is brought about in the solvent-Wax-oil mixture of lower solvent content than that required for eiicient filtration.

It is a further object of the invention to alter the normal crystallization characteristics of low wax content wax-oil mixture so that upon ltration a suciently thick wax cake will be formed to facilitate washing and handling thereof and which wax cake will have a low content of entrained oil.

Other objects and advantages of our invention will occur to those familiar with the art as the description thereof proceeds.

We have discovered that an improved wax cake may be obtained in the reverse dewaxing process as described above when employing low wax content oil-wax mixtures if a certain proportion of deoiled wax is recycled to the incoming stream of hot oil and wax before the chilling and the addition of solvent. This mixture when chilled with the addition of solvent in one or more similar increments in accordance with the limited dilution principle of the reverse dewaxing process of the above-mentioned patent, filters to give the highest yield of wax of the lowest oil content of any method known to us. It is important to po-int out that this wax which is recycled to the hot oil Wax charge may be derived directly from the filtration operation containing therefore a comparatively large quantity of solvent, or it may be recycled after the evaporation of the solvent therefrom. In either case equally satisfactory results are obtained. The essence of the effectiveness of our invention lies not alone in the formation of a thicker wax cake as might be obtained by recycling of Wax to the ltering operation vbut in the change eiected in the crystallization characteristics of the wax during the chilling step. Thus if Wax is recycled to the filtration step no change in the crystal structure and resultant type of filter cake formed. by the wax in the previously chilled oil-wax mixture is brought about, and as a consequence the lter cake, whereas it may be made to be thicker, would nevertheless possess the same undesirable properties, dense structure and high oil content. On the other hand, we have found that if this Wax is recycled to the initial step of the operation'and it is therein redisso-lved in the hot oil-wax mixture to augment the low waX content of the original feed, crystal formation upon chilling and solvent dilution, and subsequent ltration, will be considerably improved and simplified and the ease and eiciency will correspond to the treatment of a stock originally containing a higher content of high melting point wax such as for example from 15% to 30%.

As solvents for carrying out our process, that is, when the solvent is added to the Wax-oil mixture after partial or total -crystallization of the wax, We may employ such poor wax solvents as methyl ethyl ketone, butyl, amy] or propyl alcohol or mixtures thereof; various esters such ethyl acetate, ethers such as diethyl ether or isopropyl ether, chlorinated hydrocarbons such as ethylene dichloride, trichloroethylene, and other ketones such as acetone, methyl n-propyl, methyl isopropyl ketone, methyl isobutyl ketone, ethyl isopropyl ketone, methyl n-butyl ketone, and the like. In cases where high viscosity index oils are to be treated we may employ a mixture of benzene or naphtha or an aromatic solvent and any of the above solvents in order to obtain miscibility of the oil with solvents at the temperature of the second or dewaxing stage. For example, we have found that a solvent consisting of toluene, 30% methyl ethyl ketone, and 30% methyl isobutyl ketone is an excellent solvent for the second stage dewaxing and the presence oi the toluene is not detrimental for the deoiling stage because of the presence of the higher ketone, although its presence does not aid in the deoiling, and may therefore be carried through with the oil in both stages eliminating the necessity of its removal from the oil or the addition to :the oil of a diierent solvent prior to the second stage of the operation. Other solvent mixtures which we have employed successfully are for example a mixture comprising from 20% to 30% trichloroethylene plus a mixture of methyl ethyl ketone and 50% methyl isobutyl ketone; or a solvent comprising 20% trichloroethylene and 80% methyl isobutyl ketone; or a solvent comprising 40% benzene, 30% methyl ethyl ketone and 30% methyl isobutyl ketone. The last mentioned solvent is not as eiective for the dewaxing step as our iirst mentioned solvents since the yield of lo-w pour oil is somewhat lower. Whereas, solvents containing trichloroethylene as mentioned above are very good for both stages of the operation a certain amount of diiculty is encountered in the recovery of trichloroethylcne due to hydrolysis occurring on stripping with steam. The examples are not meant to limit our invention to the solvents employed inasmuch as any of the above-mentioned materials or mixtures thereof may be employed in the process.

In order to avoid confusion in the terminology of the following description we will refer to the first stage of our process as a deoiling step inasmuch as ythe prime importance thereof is the production of a high melting point, oil-free Wax. Also we will refer to the second stage of our process as a dewaxing step inasmuch as although the low melting point wax obtained therefrom may be commercially valuable the low pour point. wax free oil is the more important product.

It is sometimes desirable depending upon the characteristics of the particular feed stock to be treated to employ in the initial or deoiling step of our process a solvent which is not adequate for the second or dewaxing step of our process. Such a condition, for example, gives rise to two alternative methods of procedure. In one and perhaps the most desirable method wherein a solvent is employed in a deoiling step which does not have a sufliciently high oil solubility to dissolve the oil at the relatively lower temperatures of the dewaxing step, the solvent can be modified at an intermediate point between the two stages of the process by the addition thereto of a predetermined proportion of an aromatic hydrocarbon, petroleum naphtha, halogenated hydrocarbon or any solvent having the effect of materially increasing the solubility of the oil in said Chlor-diuor-methane. These materials in addition to diluting the oil so as to permit rapid ltration, also have the desired property of chilling the wax-oil mixture when evaporated from the solution under reduced pressure. Also if desired normally liquid solvents may be employed such as those hereinbeiore listed.

The method of operation of the process according to our invention may perhaps be better understood by reference to the description of the drawing. Referring to the drawing, a waxy stock such as for example a steam rened Louisiana bright stock or other raw distillates or ranates, containing a comparatively small percentage of wax is maintained in tank l at a temperature suiciently high to effect solution of the wax contained in the oil, such temperature for eX- ample, may be around about 150 F. This stock is drawn from tank iii vla line Il controlled byy valve I2 and pumped by pump i3 through line I4 into surge tank l5. This surge tank or a similar vessel is employed for commingling the charged and the recycled wax at a temperature suicient to eiect complete solution of the recycled wax in the oil and for this purpose may be equipped with a heating coil l 5 to maintain the temperature of the mixture suciently high to accomplish this end. The wax enriched oil is drawn from surge tank IB via line l'l, controlled by valve I8 and pumped by pump i9 into the double Wailled scraped chiller wherein the charge is cooled from the initial temperature of about 150 F. to from F. to 50 F. accompanied by the addition thereto, in one or more successive operations,

of the desired solvent. The solvent is taken from i tank 22 through line 23 controlled by valve 24 and pumped by pump 25 through line 25 wherein it may be injected into the feed within the chiller by means of the manifold valves 2l, 23, 29 or 3U.

In one specic embodiment of the process for exl ample, a feed may be cooled in the initial step to a temperature of about 120 F., at which time a quantity of the solvent as for example about 20% based on the wax-oil feed may be injected into said feed through valve 2?. diluted stock is further cooled to a temperature of about 9t F. whereafter a further quantity as for example about 20% of solvent is added thereto through valve 28, whereafter the stock is further chilled to about '75 F. and there is added thereto through valve 25 another 20% of solvent base-d on the feed and upon nal chilling to about 40 F. or 50 F. the remainder of the Solvent is added thereto through valve 35. When the addition of the solvent to the feed is made in this manner it is necessary to heat or cool said solvent as the case may be to a temperature corresponding to the temperature of the stock at the particular time of addition. It is to be understood that this addition may be made in any desired manner or sequence or it may be made at one time after the chilling has progressed to a desirable point.

The thus chilled diluted stock now in the form of a slurry passes from the chiller 20 through line 3l into separator 32 which separator may be any type desired such as for example a rotary filter. The ilter cake built up thereon is washed with further quantities of the solvent, taken from tank 22 via line 23, controlled by valve 34 and pumped by pump 35 through line 35 into separator 32. This wash solvent is introduced into the separator at the temperature of the slurry. The discharged lter cake is drawn from the separator through line 31 wherein it may be divided into two streams The partially fill by valves 38 and 42. As hereinbefore pointed out, a portion of the wax may be recycled to the initial feed stock and in this case to surge tank I6 prior to the evaporation of the solvent therefrom which recycling may be accomplished by pumping the desired proportion of the wax withdrawn from the separator through line,l 3l, and valve 38 by pump E59 through line lil returning to surge tank I6. In this case the remaining portion of the wax is discharged through valve 42 into evaporator @si wherein the solvent is evaporated from the wax passing overhead through valve 45 and line lic into condenser @l whereafter it is pumped by pump [i9 through line 50 into the solvent storage tank Z2. The solvent free wax is withdrawn from evaporator dll, through valve 52 and pumped by pump 53 through line 5e, valve 55 and line 51 into the high melting point wax storage tank 58. In the second method of operation at this point valve 33 remains closed and the entire wax discharged from the separator passes through valve to evaporator e wherein the solvent is evaporated from the wax returning to solvent tank 22 as described above, and the solvent free wax is drawn from evaporator 44 through valve 52 and is pumped by pump 53 into line 54 wherein the stream is split part of which passes through valve 55 and line e0 back to surge tank I6 to furnish the recycle wax, the remainder passing through valve 56 and line 5l to the high melting point wax storage tank 58.

Returning to separator 32, the filtrate which still contains low melting point waxes is withdrawn through line iii! controlled by valve Gl and is pumped by pump 52 through line 53 into a second chiller E4. As hereinbefore pointed out depending upon the type of solvent used in the deoiling step of the operation, it may be necessary to add to the stock prior to the deWaxing step of the operation an additional amount of a solvent such as an aromatic hydrocarbon, petroleum naphtha, halogenated hydrocarbon or the like to eiTect the solution of the oil at the lower temperatures of operation of the dewaxing step. This solvent hereinafter referred to as solvent B to distinguish it from the solvent referred to as solvent A in the initial stage of the operation is withdrawn from storage tank '55 through line 5'! controlled. by valve 68 and pumped by pump 59 into line 53 where it is commingled with the stock passing to the second operation. If, however, the solvent A employed in the deoiling operation is of such composition as to be a satisfactory solvent for the oil at the temperatures of the dewaxing operation, this addition is unnecessary. In either case the diluted stock passes from line 53 into chiller 54 wherein it is further cooled to a temperature in the neighborhood of from about 0 F. to about 15 F. passing therefrom through line 1B into separator 12 which can be any desirable type of separator such as for example a rotary filter. In case there has been no subsequent addition of solvent between the deoiling and dewaxing steps of the operation the wash solvent for the filter cake obtained in separator 'l2 may be taken directly from the storage tank 22 containing the initial solvent A. However, if as described, additional solvent is added from tank intermediate between the two stages it is necessary that the wash solvent be of the same composition as the iinal diluent entering chiller 54 in the dewaxing stage. In the latter case the wash solvent stored in tank 'I4 is drawn via line 15 chilled to temperature of separation 7 and pumped by pump 'l5 into separator 'l2 to effect the washing ofthe wax cake.

In the conventional dewaxing procedure the wax is withdrawn from separator i2 via line 83 controlled by valve Bil passing through line into evaporator 86 wherein the solvent is evaporated from the wax passing overhead through line 8l controlled by valve 88 and providing it is of the composition of the original solvent it is passed through valve 92 into condenser 93, is pumped by pump 85 from the condenser through line 95 and line 96 back to the storage of solvent A in tank 22. If, however, the solvent is of different composition than solvent A brought about as described previously by the addition of v solvent B prior to the dewaxing step of the operation it is passed through line 89, controlled by valve 99 and through line 9i to a distillation process wherein the solvent is resolved into solvent A and solvent B ess is not shown inasmuch as it does not effect the invention and. its construction will be dependent solely upon the composition of solvent A and solvent B and the necessary facilities for the resolution thereof.

A solvent free slack wax is withdrawn from evaporator 85 through line 97 controlled by valve .S8 pumped by pump 99 through line illu into the low melting point wax storage tank H32.

The dewaxed low pour point oil obtained as a filtrate in separator 72 is withdrawn therefrom through line il controlled by valve 'lil and pumped by pump 'I9 through line 86 into storage tank 82.

We have, however, discovered a method of modifying this dewaxing step whereby we are able to obtain a higher yield of low pour point oil and an essentially oil-free low melting point wax. In the conventional process as described the wax having a melting point of about 103 F. as obtained from separator 72, after removal of the solvent therefrom in evaporator 86, contains as much as 10% to 20% oil which may be recovered therefrom by means of our modification oi the process.

After removal of the wax cake from separator 'l2 and prior to introducing it to evaporator Se we may withdraw the wax cake through valve les, line i655 and pump U35 from which it passes into heater l where the wax is heated to a temperature of -35" F. Additional solvent is mixed with the wax either before heating or immediately following the heating. The solvent may be obtained from tank 65 by passing it through lines 5l and it?, thence either through valve Hi8 and line 92, if it is to be added before the wax is heated, or through valve il@ and line li i, if it is to be added subsequent to the heating operation. The mixture of wax and solvent is passed through line H2 into separator M3. The wax cake is withdrawn from separator H13 by means of pump I li through lines l l 5 and i l5, controlled by valve Hl and returned to line 85 from which it passes into evaporator 85. The ltrate containing very low melting point wax and oil is withdrawn from separator l I3 by means oi pump i IS through lines i l@ and E2G, controlled by valve l2# and passed into line 63 wherein it is mixed with the incoming feed prior to passing through Chiller fifi. The effect of this operation is to ree cover from the slack wax, obtained in the dewaxing step, an oil-ree wax with a resultant in crease in the yield of wax-free low pour point oil obtained from separator l2. It should be pointed out that we have found that the heating of the This distillation procl wax cake to 30-35a F. is an essential element for the successful operation of our modified process. Simple reslurrying of the wax cake from separator l2 with additional amounts of solvent without raising the temperature of the slurry makes the subsequent tertiary filtration ineiectual, no oiliree wax being obtained, and as a result the yield of dewaxed oil is not improved.

Because of the build upof very low melting point wax in the system resulting from this modied method of procedure it becomes necessary at intervals to byepass this tertiary ltration and proceed as shown in the drawing to evaporator 35. After a short period of total production of slack wax in this manner the system becomes cleared of the low melting point wax build up and the modied procedure may again be employed.

If for example in the process according to the drawing, 1,00() barrels per day of a steam refined Louisiana bright stock containing about 6.4% high melting point wax and about 9.7% low melting point wax were withdrawn from tank lll and charged to surge tank l5 following therefrom through the process the amount of recycle high melting point wax passed through line 40 into tank E would be in the neighborhood of about 25o barrels per day. Passing from surge tank I6 into chiller 28 wherein solvent A such as for example consisting of 49% toluene, 30% methyl ethyl ketone and 30% methyl isobutyl ketone is added to the feed in the ratio of about 3.1 to 1 based on the original charge or about 2.5 to 1 on the basis of the original charge plus the recycle Wax and proceeding through separator 32 into evaporator l/l the production of wax oi a melting point ci 166 F. is approximately 54 barrels per day. .After passing through. the second stage of the process a net yield of between 810 and S15 barrels per day of oil with a pour point of 5 1i', or less is obtained together with approximately 121 barrels per day of a slack wax melting in the neighborhood of F.

pointed out above this low melting point wax produced in the dewaxing stage of the process may c yntain anywhere from 10% to 30% of oil, but by employing our modication of the dewaX- ing stage an oil-free wax is obtained melting at about 112 F. and as a result an additional 12 to 35 barrels per day of low pour test oil is produced.

It is apparent that the process of our invention which consists of recycling a portion of the high melting point wax as obtained in the initial stage of the reverse deoilingf-dewaxing process hav 'ng the effect of increasing the wax content of comparatively low Wax content wax-oil mixtures has many advantages over the use of such process of low wax content distillates wherein recycle is not employed. The amount of wax recycled to the initial stage of the operation is a function not only oi the wax content of the initial charge but also of the optimum wax content of the nal mixture to be fed to the chiller. Although the limits for the recycle of iinished wax may not be closely deiined they are usually in the range from about 112% to about 20% added wax depending upon the wax content of the original crude waxy stock. On the basis of our work we have :found that best results are obtained if the total high melting wax content oi the charge to be treated, after the recycle of the oil-free wax to the crude waxoil stock is from about 15% to about 35% and preferably from about 20% to about 30% based on the crude wax plus added wax.

Examples of our process will serve to further almas-1e emphasize the advantages which may accrue from its use.

EXAMPLE I A Mid-Continent bright stock rainate was dewaxed by the conventional method and by the process of our invention as follows:

Run No. 1 was made by completely dissolving the waxy raffinate in 3.4 volumes of solvent consisting of methyl isobutyl ketone at 140 F. It Was subsequently chilled to 50 F. and filtered to yield 4.2% of 172 F. A. S. T. M. melting point Wax. In this run it was necessary to scrape the wax cake off of the lter mechanically since it was too thin to discharge properly. It was subsequently found that a longer filter time made no appreciable difference in the thickness or characteristics of the wax cake formed due apparently to the nature of the wax crystals precipitated in the chilling step.

A second run was made on the same stock employing the principles of our invention by blending 20% of 166 F. melting point Wax with the i'aiinate. The raffinate and added wax were heated to 140 F. to effect the complete solution of the wax in the oil whereupon it was chilled to 50 F. while adding small increments of the solvent as follows: 20%, based on the wax-oil feed at 120 F., 20% at 90 F., 20% at '75 F., and the remainder at 50 F. to give a solvent raffinate ratio of 3 to l based on the raffinate charged or 2.5 to 1 based on the raffinate plus added wax. The resulting slurry was ltered to yield 25.1% of 166 F'. melting point wax based on the charge or 6.4% based on the raffinate present representing an increase of approximately 34% in the recovery of high melting point wax from the original stock. In addition to the increased recovery the recycling of the wax greatly facilitated the filtering of the slurry which may be seen more clearly in the following table.

Table I Run number l 2 Solvent composition Methyl Isobutyl Ketone Complete dilution Limited dilution. 50 F .i 50 F.

Method of chilling. 'iirnpereture of filtration,

Vacuum n filter pick up, 8 5.

mm. g.

Fiflter rate, lbs. of wax/sq. 2.0.

Solvent Wet cake, Weight per cent of charge.

Yield of deoiled wax, weight per cent of charge.

A. S. T. M. melting point of wax.

Per cent yield based on raffinate.

It should be pointed out that the conditions chosen for run No. 1 were those that were felt to give the best comparative results with the recycle process employed in run No. 2. In attempting to employ the limited dilution principle on this and other low wax content stocks without the use of wax recycle no satisfactory product could be obtained and for this reason it was necessary to employ the complete dilution method of operation.

In the second or dewaxing step of the process the foots oil from the recycle deoiling run above was dissolved after removal of the methyl isobutyl ketone in a solvent consisting of 40% toluene, 30% methyl ethyl ketone and 30% methyl isobutyl ketone. We have found this solvent to be excellent for both the deoiling and dewaxing steps of our process but in this particular instance the deoiling step and dewaxing step were carried out independently of each other using the differ- 5 ent solvent in each case. The foots oil is cornpletely soluble in this solvent at 50 F. the temperature at which it is discharged from the filter of the deoiling stage. This solution was subsequently chilled to 5 F. and filtered yielding 87.05% of solvent free oil. The wax cake was repulped at 35 F. in accordance with the principles of our modied dewaxing procedure as hereinbefore disclosed in the presence of an added quantity of solvent and filtered to yield 6.9% of oil free Wax with an A. S. T. M. melting point of 112 F. The filtrate was recycled to the initial stage of the dewaxing step wherein it was again chilled to 5 F. and ltered again yielding an additional 2.6% of low pour point oil and 3.4% of 90 F. melting point Wax. These values may be summarized and compared to the two stage proces-s in which Wax recycle was not employed in the deoiling step and the conventional dewaxing step in which no repulping of slack wax from 25 secondary filtration was employed.

Table II g Ciivelll'tional coi mgargelgggifd Dewaxing Yield of high melting point Wax, Wt.

percent 6. 4 4. 2 Yield of 5 F. pour point oil, Wt. 83.9 81.5 percent Yield of low melting point Wax 1 9. 7 2 14.3

l 6.4% 112 F. and 3.3% 90 F. melting point oil-free waxes. 2 Slack Wax containing approximately 20% oil and melting at 105 F.

EXAMPLE II Another series of deoiling runs were made on an Eastern low Wax content stock to compare the methods of operation. In the first run 400 volumes of waxy raffinate Was combined with 100 volumes of wax of 166 F. melting point which dissolved in the raffinate at the initial operating temperature of 140 F. This solution was chilled to F. adding solvent consisting of 40% toluene, 30 methyl ethyl ketone and 30 methyl isobutyl ketone as follows: 10% based on the feed at 125 F., 10% at 90 F., 20% at 60 F. and the remainder at 40 F. to give a solvent to feed ratio of 3.0 to 1. This slurry was filtered at 40 F., the cake Was Washed to yield 24.1% of wax of 167 F. melting point based on the charge or 6.53% based on the waxy raffinate, which represents a lter rate of 2.2 pounds of solvent free wax per square foot of filter space pei` hour or 0.62 pound of product Wax per square foot per hour.

In the second of these runs 50 volumes of waxoil feed was dissolved in 150 volumes of the solvent and the mixture chilled to 40 F. and filtered to give 6.2% wax of 167 F. melting point. The lter rate in this run, in which no wax recycle was employed was only 0.53 pound of solvent free wax per square foot of filter area per hour.

These examples are illustrative of the process of our invention but are not meant to limit its scope as many modifications thereof will occur to those skilled in the art without departing from the principles of the Wax recycling in the deoiling stage or the repulping in the dewaxing stage as set forth in the following claims.

We claim:

1. In a two stage process for separating wax- 1 l oil mixtures which comprises a deoiling step and a dewaxing step, the deoiling step comprising bringing said mixture to a state wherein the wax is substantially completely dissolved in the oil, cooling said wax oil solution in the absence of any substantial amount of diluent to a temperature sufficiently low to crystallize a portion of the wax and to produce a mass which is iluid at said cooling temperature, commingling said cooled fluent wax-oil mass with a solvent at substantially the same temperature as said wax-oil mixture to dissolve the oil present, and separating a filtrate comprising the solvent solution of oil from the crystallized wax, the improvement comprising recycling a portion of said separated crystallized wax to the initial stage of the operation wherein said wax is redissolved in the oil-wax charge thereby increasing the Wax content ci said charge, the dewaxing step comprising further chilling 'the ltrate from the deoiling step of the operation so as to crystallize the low melting point wax therein, separating the wax from the oil-solvent mixture in an initial separator, the improvement comprising repulping said low melting point wax at a temperature substantially above the dev-.faxing temperature in the presence of additional amounts of solvent, separating the wax from a filtrate comprising the oil-solvent solution in a secondary separator to give a substantially oilfree wax of higher melting point than the wax obtained directly from said initial separator in the dewaxing step and recycling the filtrate from this secondary separator to the chiller in the dewaxing step, and recovering a substantially wax free, low pour point oil from the initial separation.

2. In a process for separating wax-oil mixtures which comprises the chilling of said waxoil mixtures in the presence of a diluent so as to crystallize substantially all of the wax contained therein, separating the wax from the oilsolvent mixture in an initial separator, the improvement comprising repulping the said separated wax at a temperature substantially above the temperature of said initial separation in the presence of additional amounts of diluent, separating the resultant wax-oil solvent mixture in a secondary separator to give a substantially oil freewax of higher melting point than the wax obtained directly from said initial separation, and recycling the separated oil from said secondary separation to the incoming feed stream, and recovering a substantially wax free low pour point oil from said initial separation.

3. A process as in claim 1 wherein the solvent employed in the deoiling step is recovered from the filtrate from the deoiling step comprising the solvent solution of oil separated from crystalline wax and a secondary solvent is added to the solvent free oil prior to the dewaxing step.

4. A process as in claim 1 wherein the ltrate from the separation stage of the deoiling step, which is a filtrate comprising the solvent solution of oil separated from the crystallized wax, is further diluted with an oil solubility increasing compound prior to the dewaxing step.

5. In a two-stage process for separating waxoil mixtures which comprises a deoiling step and a dewaxing step, the deoiling step comprising bringing said mixture to a state wherein the wax is substantially completely dissolved in the oil, cooling said wax-oil solution to a temperature suciently low to crystallize a portion of 1'2 the wax and to produce a mass which is uid at said cooling temperature, commingling said cooled fluent wax-oil mass with a solvent at substantially the same temperature as said wax-oil mixture to dissolve the oil present, which solvent comprises a major proportion of at least one ketone characterized by the presence of from 5 to 6 carbon atoms in its molecular structure and at least one ketone characterized by the presence of from 3 to 4 carbon atoms in its molecular structure and a minor proportion of a compound selected from the class of compounds consisting of aromatic hydrocarbons, petroleum naphthas and halogenated hydrocarbons, and separating a filtrate comprising the solvent solution of oil from the crystallized wax, the improvement comprising recycling a portion of said separated crystallized wax to the initial stage of the operation wherein said wax is redissolved in the oil-wax charge thereby increasing the wax content of said charge, the dewaxing step comprising further chilling the nltrate from the deoiling step of the operation so as to crystallize the low melting point wax therein, separating the wax from the oil-solvent mixture in an initial separator, the improvement comprising repulping said low melting point wax at a temperature substantially above the dewaxing temperature in the presence of additional amounts of solvent, separating the wax from the oil solvent solution in a secondary separator to give a substantially oil-free wax of higher melting point than the wax obtained directly from said initial separator in the dewaxing step and recycling the filtrate from said secondary separation to the chiller in the dewaxing step, and recovering a substantially wax-free, low pour point oil from the initial separation.

6. A process according to claim 5 wherein the solvent employed in the deoiling step comprises a mixture of at least one ketone characterized by the presence of from 5 to 6 carbon atoms in its molecular structure and at least one ketone characterized by the presence of from 3 to 4 carbon atoms in its molecular structure Which solvent is modied in the dewaxing step by addition to the filtrate from the deoiling step of a minor proportion with respect to the ultimate solvent composition of a compound selected from the class of compounds consisting of aromatic hydrocarbons, petroleum naphthas, and halogenated hydrocarbons.

P. STANLEY BACKLUND. BYRON M. BEILDECK.

CITED The foilowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,881,643 Jones Oct. 11, 1932 2,036,188 Anderson Apr. 7, 1936 2,053,872 Montgomery Sept. 8, 1.936 2,166,891 Gee I July 18, 1939 2,229,658 Jenkins Jan. 28, 1941 2,229,659 Carr Jan. 28, 1941 2,248,668 Gee II July 8, 1941 2,281,667 Bray May 5, 1942 2,284,607 Marshall May 26, 1942 2,330,740 Pokorny et al Sept. 28, 1943 

